The recognition of inflamed bronchi or bronchioles was never difficult. In the gross the presence of the abnormal exudate and the intense injection of the mucosal surfaces always attracted attention to the inflammatory state. Furthermore where the mucosa had been desquamated the surface of these tubes was found to be quite granular if closely observed. With moderate magnification by means of a hand lens the granular appearance was shown to be due to the engorged vessels. Much easier, of course, was the recognition of the inflammatory reaction by the microscope. The importance, however, of the bronchitis and bronchiolitis lay in the amount of involvement which had occurred in the neighboring tissues. As we, however, indicated elsewhere, we do not doubt that many of the cases of three-day fever have a state of tracheitis and bronchitis equal to that which we have observed in many of our cases. Whether the inflammatory reaction progressed beyond the firmer bronchial tubes to the softer and more vascular structures would be difficult to say where our evidence rests upon the clinical findings alone. It is, however, probable that a certain number of the severe and sharp attacks of influenza not only cause a tracheitis and bronchitis of the larger tubes, but also extend more deeply into the smaller ramifications tending to simulate the reactions which we have above described. When we ask ourselves, however, how distantly must the infection invade the smaller bronchial tubes before involving the parenchymatous tissues of the lung we are at a loss to enunciate a general rule. It is more than probable that there are modifying influences which determine whether the bronchitis with a certain amount of its bronchiolitis will progress to a true pneumonia or will remain localized to these tubular systems. I can well appreciate that in the event that a bronchitis has an inflammatory reaction accompanied by much serous exudate there is great danger of flooding the neighboring alveoli with this inflammatory fluid and of carrying the large numbers of the micro-organisms within the tubes to the air sacs of the lung. Under these conditions the virus has an unusual ability to develop the disease from one localized in the air passages to that of a true pneumonia. It is probable that the peculiar early acute reaction which is present in the air passages in epidemic influenza is responsible for the extensive involvement of the lung in the severe and dangerous form of inflammation. TABLE VI. EXTENT AND DISTRIBUTION OF PNEUMONIA.